A universal joint apparatus is used for transmitting rotation or power between two shafts which are not disposed on a straight line. A cross universal joint referred to as a Cardan joint, a hook joint, a cross joint or the like is constituted by coupling two shafts via a cross member having four shaft portions in a cross-like shape. The two shaft portions disposed on sides opposed to each other are supported by yokes of the respective shafts.
A universal ball joint interposes a torque transmitting ball at guide grooves formed at an inner face of an outer joint member and an outer face of an inner joint member fitted thereto, respectively, to thereby transmit power between two shafts provided with the inner and the outer joint members.
Whereas according to the constant velocity ball universal joint, rotation between two shafts is made an equal velocity even when there is an intersecting angle therebetween, on the other hand, the cross universal joint is provided with a drawback derived from mechanics that rotation between two shafts is not made an equal velocity when there is an intersecting angle therebetween. In order to eliminate the drawback, when the cross universal joint is used as a joint apparatus, in many cases, two sets thereof are used as a pair of combination by interposing an intermediate shaft. In this case, it is necessary to integrate the two sets such that respective intersecting angles thereof are made to be equal to each other and phases in rotational directions of two cross members are set to a predetermined relationship.
According to a steering apparatus of a vehicle, when vibration from a road face is transmitted to a handle (steering wheel), steering feeling is deteriorated. Therefore, vibration from the road face is devised not to be transmitted to the steering wheel by providing a shock absorber. Normally, a rubber joint apparatus interposing vibration isolating rubber between the two shafts is used for such a shock absorber as a countermeasure against vibration. When the rubber joint apparatus is provided at an intermediate shaft of the joint apparatus, a torsional rigidity thereof is comparatively low owing to a structure thereof. Therefore, when the steering wheel is rotated by a strong force, the rubber joint apparatus is significantly twisted. Therefore, the above-described phases in the rotational directions of the two cross members are deviated from each other, equal velocity performance which is to be achieved by combining the cross universal joints is deteriorated. As a result, a variation in a transmission torque is brought about. The operation also deteriorates steering feeling.
Further, since the rubber joint apparatus is assembled with the vibration isolating rubber and other parts, and there are large numbers of related many parts, the apparatus is accompanied by considerably large fabrication errors. Owing to the errors, the equal velocity performance which is to be achieved by combining the cross universal joints in consideration of the phases is deteriorated, which amounts to a variation in the transmission torque and a deterioration in the steering feeling. Although the errors are resolved for the time being by promoting accuracy of the rubber joint apparatus and parts related thereto, or selecting combinations of individual parts to integrate (matching), such a countermeasure is not preferable in view of cost. Although the vibration isolating rubber member is provided with a stopper which is operated against a constant amount or more of torsion, when a stopper angle thereof is reduced in order to promote accuracy, there also poses a problem that it is difficult to achieve a constitution which can be satisfied in view of a vibration isolating function.
(Patent Reference 1)
JP-A-2000-257645
(Patent Reference 2)
JP-UM-B-7-43494
(Patent Reference 3)
JP-UM-B-3-25445
Although when used in a steering apparatus, a female joint member is coupled to an input shaft or an output shaft (for example, intermediate shaft) therefor integrally or by a connecting base member integral with the female joint member, it is ordinary that a male joint member is integrally formed with the input shaft or the output shaft therefor. However, for convenience of design of other part, also a member coupled with the input shaft or the output shaft becomes a male shaft. Although in this case, a coupling for coupling the shafts is needed, when constituted in this way, a rotational diameter of the joint portion is increased. Further, when a shaft length is obliged to set to be short, there is a case in which the coupling cannot be put therebetween. Therefore, there is a case that such attaching method cannot be adopted. Further, in this case, the coupling needs to be prepared separately and therefore, cost is increased by the coupling per se and integration thereof.
Further, the above-described ball guide groove needs to be subjected to highly accurate finish grinding (polishing) since the torque transmitting ball is rolled. However, the ball guide groove on a side of the female joint member is formed at inside of an inner space such that the torque transmitting ball and an outer spherical face joint portion of the male joint member are contained to an inner portion thereof. Further, since the space is formed at an end portion of the input shaft or the output shaft which is integrally solid and therefore, the space is necessarily provided with a bottom portion. That is, a groove having an inner wall face of a bottomed hole needs to be accurately ground. It is not inherently easy to grind the inner wall face of the bottomed hole, further, the groove at inside thereof needs to be accurately ground and therefore, it is a current state that time and cost are taken in grinding the ball guide groove on the side of the female joint member.
{Patent Reference 4}
JP-A-2002-114155
The present invention is an invention which has been carried out in view of the above-described problem and it is a first problem thereof to provide a joint apparatus for a vehicular steering apparatus in which a variation in a steering torque is inconsiderable, a vibration isolating function is excellent and fabrication cost is inexpensive.
Further, the present invention is an invention which has been carried out in view of the above-described problem and it is a second problem thereof to provide a universal ball joint for a vehicular steering apparatus capable of being coupled with a counterpart of coupling without separately preparing a coupling even when the counterpart of coupling is a shaft (male shaft), constituting a coupling portion on a side of a female joint member and a space of an inner spherical face joint portion by a through hole, and capable of easily grinding a ball guide groove. Further, it is a third problem thereof to provide a universal ball joint at inexpensive cost thereby.